This invention relates to chromium plating, and more particularly to electrolytic chromium plating wherein chromium in a chromium plating bath solution is electrodeposited on the article plated.
Over the years, a number of different plating bath solutions have been proposed for chromium electrodeposition. A commonly used bath solution is a chromic acid bath, resulting from dissolving CrO.sub.3 in water, and which further contains a sulfate catalyst, or a mixture of catalysts, such as sulfate and silicofluoride.
This invention is bottomed on the discovery that the addition of alcohol, i.e., methyl or ethyl alcohol, to a chromium plating bath solution containing dissolved chromium electrolyte significantly increases the current efficiency realized during the plating process. A further advantageous result is that chromium platings or coatings are produced tending to have a more uniform thickness, which offers the possibility of reducing the required thickness of a plating in a given application. It has also been observed that the inclusion of the alcohol affects the initial stages of chromium deposition, by speeding up the plating that occurs. By including alcohol in the bath solution, improved results are obtained from bath solutions containing the usual catalysts, and electrodeposition of chromium has been obtained utilizing bath solutions devoid of conventional catalyst. Particularly good current efficiencies have been observed in electrolytic platings performed using plating bath solutions containing a mixture of dissolved metallic electrolytes, such as dissolved chromium and iron electrolytes, to produce by electrodeposition alloy coatings.
A general object of this invention, therefore, is to provide an improved electrolytic process of chromium plating, and improved chromium plating bath solutions.
More particularly, an object of the invention is to provide improvements in an electrolytic process of chromium plating, and a chromium plating bath solution, which relies upon the incorporation in the bath solution of methyl or ethyl alcohol.
Various other objects, advantages and features of the present invention will become more fully apparent from a reading of the following description, which is to be taken in conjunction with accompanying examples included for the purpose of illustration.